The present disclosure generally relates to a calorimetric composition. The colorimetric composition is an indicator of exposure to light, and in particular, ultraviolet radiation (“UV”). Also disclosed are methods for preparing and using the same.
Plastic, polymeric, or elastomeric components are a part of everyday life. However, these materials are susceptible to degradation when exposed to the elements of light, water, and oxygen. For example, outdoor exposure of plastic resins may lead to embrittlement and cracking. When oxidation due to photochemical processes occurs in the polymer, chemical bonds break and the polymer begins losing molecular weight. If not chosen and used correctly, some plastic materials will degrade and lose their mechanical properties. When a failure occurs, it can be dangerous and costly.
As a result, it is recognized that outdoor exposure to large amounts of sunlight radiation may cause problems and that such exposure should be monitored. For example, polyethylene tanks are routinely used for bulk chemical storage outdoors. General safety guidelines call for inspection after several years of service for crazing, cracking, and discoloration. One suggested method of monitoring the integrity off such polyethylene tanks involves treating a small area with a colored dye, then watching for voids, formed as a result of photochemical degradation, to take up the dye.
Additionally, in order to minimize the deleterious effects of sunlight to these tanks, polyethylene can be stabilized to a certain degree. This is done with either UV absorbers and hindered amine light stabilizers (HALS) or high loadings of carbon black (3%). For example, UV absorbers are substances that absorb UV radiation energy, then dissipate the energy in a harmless form. They are used in plastics and rubbers to decrease light sensitivity. Hindered amines and carbon black can also be utilized to stabilize polymers against sunlight.
Furthermore, a United Nations report outlined a proposal to mitigate the risk of UV exposure of plastics or polymers commonly used in Intermediate Bulk Containers (IBCs). It was recognized that cumulative exposure to sunlight can reduce the strength of such containers which may be used to transport dangerous goods. An elaborate coding system was proposed to guide users on how certain plastics or polymers should be labeled and transported in an effort to minimize outdoor exposure.
Another area of failure of plastics or polymers in the field involves warranties established by original equipment manufacturers (“OEMs”) of such components. Some resins are designed for outdoors use while others are not. However, these unstable and unsuitable resins are often used in outdoor settings anyways. Manufacturers of outdoor equipment may void the warranty if the parts are exposed to excessive sunlight.
Accordingly, an easy and reliable method of inspecting warranty claims and performing preventive maintenance is needed. Radiometers could solve some of the outlined problems, but are expensive and fragile. A simple calorimetric approach would aid inspections and facilitate product reviews by test organizations.
A composition is needed which, upon exposure to UV light, forms a chromophore that is stable with respect to continued UV exposure, quantifiable, and/or cost effective. The composition could be used as a colorimetric indicator of sunlight exposure.
Several articles have been designed to indicate sunlight exposure, but they generally focus on short-term exposure. These systems usually involve Bronsted acid-base reactions where an acid-sensitive dye is protonated and changes through multiple colors within a short period of time, e.g. 60 minutes, as in U.S. Pat. No. 5,028,792. These systems are not known to be lightfast, so retention of the long-term exposure information is lacking. Other systems rely on the photochemical degradation of a chlorine-containing polymer to produce acid, followed by protonation of an acid-sensitive dye, as in U.S. Pat. No. 3,743,846. This system operates when exposed to gamma rays or electron rays. Additional examples rely on an organic halogen to produce acid necessary for dye protonation and a subsequent color shift. These systems are used as UVB sensors for short-term exposure, as in U.S. Pat. No. 6,504,161.
It would be desirable to produce a new composition which can provide an indication of exposure to sunlight or to UV radiation, such as for use under long term exposure.